The present invention relates to the field of peptide immunotherapy. In particular, the invention provides novel methods and materials for efficiently treating patients having an HLA-B*0702 phenotype.
Immunotherapy is a therapeutic approach which is currently the subject of a great deal of interest in the context of the treatment of cancer. The principle thereof is based on immunization with peptides which reproduce T cell epitopes of tumor antigens recognized by cytotoxic T lymphocytes (CTLs) which play a major role in the elimination of tumor cells.
It will be recalled that CTLs do not recognize whole protein antigens, but peptide fragments thereof, generally comprising 8 to 11 amino acids, presented by class I major histocompatibility complex (MHC I) molecules expressed on the surface of cells. The presentation of these peptides is the result of the antigen processing which involves three steps:                cytosolic degradation of the antigen by a multienzyme complex called proteasome        translocation of the peptides derived from this degradation in the endoplasmic reticulum (ER) by the TAP transporters        association of these peptides with the MHC I molecules and exportation of the peptide/MHC I complexes to the cell surface        
The peptide/MHC I complexes interact with the specific T cell receptor (TCR) on CTL inducing the stimulation and amplification of these CTL which become able to attack target cells expressing the antigen from which the peptide is derived.
During the antigen processing, a peptide selection takes place, which results in a hierarchy of peptides presentation. Peptides that are preferentially presented by the MHC I molecules are called immunodominant while peptides that are weakly presented are called cryptic. Immunodominant peptides exhibit a high affinity for the MHC I and are immunogenic while cryptic peptides exhibit a low affinity for MHC I and are non-immunogenic.
Immunodominant peptides have widely been targeted by tumor vaccines in preclinical and clinical studies with disappointing results (Bowne et al., 1999; Colella et al., 2000; Gross et al., 2004; Hawkins et al., 2000; Naftzger et al., 1996; Overwijk et al., 1998; Vierboom et al., 1997; Weber et al., 1998).
Tumor antigens are frequently self proteins over-expressed by tumors and expressed at lower levels by normal cells and tissues. Immune system is unable to react against these self antigens because of the self tolerance process. Self-tolerance concerns mainly the immunodominant peptides (Cibotti et al., 1992; Gross et al., 2004; Hernandez et al., 2000; Theobald et al., 1997) thus explaining the incapacity of these peptides to induce a tumor immunity.
Cryptic peptides are much less involved in self tolerance process (Anderton et al., 2002; Boisgérault et al., 2000; Cibotti et al., 1992; Friedman et al., 2004; Gross et al., 2004; Moudgil et al., 1999; Overwijk et al., 2003; Sinha et al., 2004) and can therefore induce an efficient tumor immunity providing their immunogenicity is enhanced (Disis et al., 2002; Dyall et al., 1998; Engelhorn et al., 2006; Gross et al., 2004; Grossmann et al., 2001; Lally et al., 2001; Moudgil and Sercarz, 1994a; Moudgil and Sercarz, 1994b; Palomba et al., 2005).
The usual strategy for enhancing the immunogenicity of cryptic peptides, that because of their low MHC I affinity are non-immunogenic, consists in increasing their affinity for the MHC I molecules via amino acids substitutions. Peptide affinity for MHC I molecules mainly depends on the presence at well defined positions (primary anchor positions) of residues called “primary anchor residues”. These residues are MHC I allele specific. The presence of primary anchor residues although often necessary is not sufficient to ensure a high MHC I affinity. It has been shown that residues located outside the primary anchor positions (secondary anchor residues) may exert a favourable or unfavourable effect on the affinity of the peptide for the MHC I (Parker et al., 1994; Rammensee H et al., 1999). The presence of these secondary anchor residues makes it possible to explain the existence, within the peptides having the primary anchor motifs, of a great variability in the binding affinity.
Amino acids substitutions aiming at enhancing affinity for MHC I molecule should preserve the antigenicity of such optimized peptides. CTL generated by optimized peptides should cross-react with the corresponding native peptides.
Many teams have succeeded in further enhancing immunogenicity of already immunogenic peptides by increasing their affinity for HLA-A*0201 (Bakker et al., 1997; Parkhurst et al., 1996; Sarobe et al., 1998; Valmori et al., 1998). The inventors have previously described a general strategy to enhance affinity and immunogenicity of HLA-A*0201 restricted cryptic peptides (Scardino et al., 2002; Tourdot et al., 2000).
HLA-B*0702 is a frequently expressed molecule (25% of the population). Identification and optimization of HLA-B*0702 restricted tumor cryptic peptides should therefore be necessary in order to develop efficient cancer vaccines for HLA-B*0702 expressing patients.
Few tumor peptides presented by HLA-B*0702 have been described to date. Two peptides derived from the CEA (CEA632) (Lu et al. 2000) and TERT (TERT1123) (Cortez-Gonzales et al. 2006) antigens have been identified; these peptides exhibited a strong binding affinity for HLA-B*0702 and were immunogenic both in HLA-B*0702 transgenic mice and in vitro tests with human cells. These experimental results show that these peptides are immunodominant peptides.
Two additional peptides derived from MAGE-A 1 (MAGE-A1289) (Luiten et al., 2000) and RU2 (a new antigen expressed by renal cell carcinoma) (Van den Eynde et al. 1999) have been identified to be targets of HLA-B*0702 CTL that had been isolated from cancer patients. Although there is no information about the HLA-B*0702 affinity of these two peptides, we can consider them immunodominant because CTL developed in cancer patients are always directed against immunodominant peptides.